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New Avenues for Function Control and Application Development of Fullerenes (Press Release)

Release Date
21 Jun, 2010
  • BL02B1 (Single Crystal Structure Analysis)
A research group consisting of Professor Hiroshi Sawa, Associate Professor Eiji Nishibori, and Assistant Professor Shinobu Aoyagi of Nagoya University, succeeded in the single-crystal structure determination of a spherical molecule of endohedral C60 fullerene containing lithium ion (Li@C60), which was synthesized in a large quantity (several million times larger than the conventional quantity) and refined (highly purified) by a newly developed method using the Single-Crystal Structure Analysis Beamline (BL02B1) at SPring-8 for the first time in the world.

– First-Ever Success in Large-Scale Synthesis and Single-Crystal Structure Determination of Endohedral C60 Fullerene Containing Lithium Ion -

Nagoya University
Tohoku University
Ideal Star Inc.
Japan Synchrotron Radiation Research Institute
RIKEN

A research group consisting of Professor Hiroshi Sawa, Associate Professor Eiji Nishibori, and Assistant Professor Shinobu Aoyagi of Nagoya University (Michinari Hamaguchi, President), succeeded in the single-crystal structure determination of a spherical molecule of endohedral C60 fullerene containing lithium ion (Li@C60),*1 which was synthesized in a large quantity (several million times larger than the conventional quantity) and refined (highly purified) by a newly developed method using the Single-Crystal Structure Analysis Beamline (BL02B1) at SPring-8 for the first time in the world. This was achieved through a joint research with groups led by Professor Hisanori Shinohara of Nagoya University and Professor Hiromi Tobita of Tohoku University (Akihisa Inoue, President), and scientists of Ideal Star Inc. (Yasuhiko Kasama, Representative Director), Japan Synchrotron Radiation Research Institute (JASRI; Tetsuhisa Shirakawa, President) and RIKEN (Ryoji Noyori, President). These achievements will accelerate the industrial utilization and application of various endohedral metallofullerenes such as Li@C60.

This study showed the possibility of the stable supply and industrial application of the high-purity sample of endohedral metallofullerene using C60 fullerene as a material, which is synthesized in a large quantity. This is a pioneering report on the research on C60-based metallofullerenes, which will be widely discussed in the future, opening new avenues for the function control and application development of fullerenes.

Expectation for Li@60
C60 fullerene, first discovered in 1985, is a soccer-ball-shaped hollow spherical molecule with a diameter of 1 nm (1 nm is a millionth of a mm) consisting of 60 carbon atoms. Recently, the industrial application of C60 fullerene as a major nanotechnological material has progressed in a wide range of fields such as electronic device manufacturing, energy, environment and medical care. This is because the large-scale synthesis of C60 fullerene has become possible and its unique property has been extensively studied worldwide and nearly clarified. Since the discovery of C60 fullerene, it has been considered that its function and property can be controlled and expanded by incorporating a metal atom into the hollow fullerene molecule. Many researchers all over the world have attempted the incorporation of metals into C60 fullerene. While the existence of C60-based metallofullerenes has been reported from the beginning, the isolation of the molecule and the determination of its molecular structure have not been successful until today, 20 years after the discovery, because the molecular reactivity is increased by the incorporation of metals. The isolation and molecular structure determination of high-order endohedral metallofullerenes such as those of C80 and C82 fullerenes with more than 60 carbon atoms have been reported, but the application development of such molecules is very difficult because they are synthesized in extremely small quantities. However, the research on such high-order endohedral metallofullerenes has suggested the possibility of the property control by the incorporation of metals into fullerenes, raising expectations for the progress of the research on C60-based metallofullerenes.

Quantity synthesis, structure determination and stable supply
Ideal Star Inc. and the research group of Professor Tobita at Tohoku University succeeded in synthesizing Li@C60 with a high yield by an original method called the plasma shower method,*2 and completely isolated and crystallized Li@C60 molecules. The amount of synthesis per unit time is several million times larger than that by the conventional method. Also, the organization of the supply system will open up the avenue for the industrial application of Li@C60.

To demonstrate that the C60 fullerene molecule in the synthesized crystal contains a lithium ion, the research group of Professor Sawa at Nagoya University conducted a high-resolution single-crystal X-ray diffraction*4 experiment using a large cylindrical imaging plate (IP) camera*3 of the BL02B1 Beamline at SPring-8. They demonstrated that Li@C60 contains a lithium ion, and determined the molecular structure of Li@C60. Since lithium is an extremely light element of atomic number 3 and it is easily ionized and electrochemically activated, it is used in various fields of industry such as in ion batteries. However, it is generally difficult to examine the precise spatial state of this element due to its lightness. It is possible only by X-ray diffraction measurement using the high-brilliance X-rays at SPring-8. As a result of a detailed analysis called electron density analysis, a lithium ion incorporated in the C60 fullerene was observed, verifying the success in the isolated synthesis of Li@C60. Moreover, the lithium ion in Li@C60 was located 0.13 nm off the center, showing that Li@C60 is completely different from the inert gas molecules such as H2 and Ar. The two-dimensional arrangement of the electrically polarized Li@C60 molecules in the crystal strongly suggested the possibility of the application of Li@C60 as a single-molecule switch and a ferroelectric thin film, which has been expected on the basis of many theoretical predictions.

Expectations for industrial application
The global competition for the development of organic solar cells, the next-generation solar cells that will replace silicon (Si) solar cells, is increasing. Considering the considerable flexibility and the various utilization forms of C60 fullerene, it is necessary for the development of organic solar cells to use C60 fullerene that can swiftly remove an electron from an exciton excited by light in the active region and separate the free electron from the hole. The appearance of Li@C60 that is found to pull out an electron with a smaller energy than that with C60 fullerene will open up a new possibility to enhance the performance of organic solar cells. Increases in the speed and stability of switching are also required for organic transistors used in flexible displays such as organic electroluminescence (EL) displays and liquid crystal displays. Moreover, while the fullerenes containing alkali metals are organic molecular materials, they show electron conductivity similar to that of n-type semiconductors. It is expected that Li@C60 will be widely used as a functional nanotechnology material for enhancing the performance of these organic electronic elements.

The use of C60 fullerene in contrast media and physiologically active materials has been conventionally attempted in the field of medical care. In addition to that field, there is a possibility that Li@C60, as a ferroelectric molecule generated by the incorporation of alkali metals, will be used in ultrahigh-density memories of more than 500 Tbit/in2 with a molecule of 1 nm diameter as one cell. The research on the application of Li@C60, the structure and electronic property of which were clarified in this study, will be further accelerated in a wide range of fields opened up by nanotechnology.

These research achievements were published in the online version of the British scientific journal Nature Chemistry on 20 June 2010.

Publication:
"A Layered Ionic Crystal of Polar Li@C60 Superatoms"
Shinobu Aoyagi, Eiji Nishibori, Hiroshi Sawa, Kunihisa Sugimoto, Masaki Takata, Yasumitsu Miyata, Ryo Kitaura, Hisanori Shinohara, Hiroshi Okada, Takeshi Sakai, Yoshihiro Ono, Kazuhiko Kawachi, Kuniyoshi Yokoo, Shoichi Ono, Kenji Omote, Yasuhiko Kasama, Shinsuke Ishikawa, Takashi Komuro and Hiromi Tobita
Nature Chemistry 2, 678–683 (2010), published online 20 June 2010



<Figure>

Fig. 1 Layered crystal structure of [Li@C60](SbCl6)
Fig. 1 Layered crystal structure of [Li@C60](SbCl6)

Purple: lithium ion; green: C60 fullerene; orange: SbCl6. Li@C60 molecules and SbCl6 molecules are two-dimensionally arranged in a pair.


Fig. 2 Molecular structure of Li@C60 determined in this study
Fig. 2 Molecular structure of Li@C60 determined in this study

(a) and (b) are the molecular structures from different viewpoints.
The lithium ion indicated in purple is located near the six-membered ring 0.13 nm off the center of the C60 fullerene molecule indicated in green.
(c) Position of Li@C60 and two SbCl6 (orange) coordinated in vicinity. A lithium ion occupies one of the two positions near the Cl atoms adjacent to the C60 fullerene with equal probability.


<Glossary>

*1 Endohedral C60 fullerene containing lithium ion (Li@C60)
Soccer-ball-shaped spherical C60 fullerene molecule consisting of 60 carbon (C) atoms containing a lithium (Li) atom in its molecular cage denoted as Li@C60. While it has been synthesized since the 1990s, its molecular structure has not yet been clarified.

*2 Plasma shower method
Method to obtain Li@C60 by reacting lithium ion plasma generated in vacuum with C60 fullerene on negatively biased substrate. Ideal Star Inc. originally developed this method on the basis of the fundamental research by Professor Rikizo Hatakeyama and his colleagues at Tohoku University.

*3 Large cylindrical imaging plate (IP) camera of BL02B1 Beamline at SPring-8
X-ray diffraction apparatus for precise single-crystal structure analysis that was installed in the Single-Crystal Structure Analysis Beamline (BL02B1) at SPring-8 in March 2008. The X-ray detector is a large cylindrical IP with an automatic reading function. A large amount of X-ray diffraction data of a wide angular range can be collected with high accuracy and high efficiency.

*4 Single-crystal X-ray diffraction
X-ray diffraction is a method of determining the atomic arrangement in a crystal (crystal structure) and the electron distribution (electron density distribution) on the basis of the X-ray scattering pattern obtained by irradiating X-rays on crystals (X-ray diffraction pattern). When a single crystal is used as the sample, it is called single-crystal X-ray diffraction. Compared with powder X-ray diffraction, in which powder is used as the sample, the difficulty in the preparation of samples and the long period of time required for the measurement are the disadvantages. On the other hand, the small overlap of diffraction peaks and the high diffraction intensity are the advantages.



For more information, please contact:
Prof. Hiroshi SAWA (Nagoya University)
E-mail: mail

Prof. Hiromi TOBITA (Tohoku University)
E-mail: mail

idealStar inc.
E-mail: mail

Dr. Kunihisa SUGIMOTO (JASRI)
E-mail: mail